Stains that develop on hard vitreous surfaces, e.g., lavatories, tubs, toilets, etc., are often extremely difficult to remove. Where such stains develop because of the deposition of hard water salts, and/or iron residues combined with organic components (fecal and algal), removal can be especially difficult. Powdered abrasive cleansers have traditionally been used to treat such stains. However, in recent years, liquid or gel cleaners have been especially developed for removal of such stains; and most usually such cleaners, along with customary surfactant and detergent components, incorporate relatively strong acid and abrasive components. The acid component is quite useful in attacking the hard water components of the stain and helps in hydrolyzing the organic matter. The abrasives, with the aid of a scrubbing action, are effective in physically removing the stains from the surface. Together, the detergents and surfactants, along with the acids and abrasives, can be quite effective in cleaning such stained surfaces.
One example of a thickened cleaner is disclosed in U.S. Pat. No. 3,997,460 issued Dec. 14, 1975 to Sirine et al. The referenced patent describes a thickened abrasive cleaner which is effective for removing stains on hard surfaces. The product includes a mineral acid as well as an abrasive suspended in the cleaner to aid in the mechanical removal of stains. The formula utilizes fumed silica as a thickening agent and is contended to suspend the abrasive particles in the liquid components over extended periods of time.
The disadvantages of cleaners such as the Sirine et al cleaner are at least twofold. It is difficult to maintain a desirable viscosity which is also capable of suspending abrasives. It is also difficult to produce a cleaner which little or no syneresis, i.e., whose liquid components do not substantially separate from the solid components in the cleaner.
As an example of the first disadvantage, one difficulty with the Sirine et al composition is the development of increasing viscosity as the product ages. Such formulations become increasingly more viscous as they sit on the shelf--and, in fact, eventually become so viscous that they gel. Then they are no longer able to be poured or squeezed from their containers. Such products therefore have a poor "shelf" life, and for that reason have not been commercially exploited. Such compositions utilized fumed silica thickening components, but the undue thickening occurs even where the fumed silica is present in the range of about 1-5% by weight. At the upper 5% limit, increased thickening occurs very rapidly and the product soon "sets up" into the aforementioned rigid "gel". On the other hand, as shown below, 5% or less precipitated silica provides little viscosity and will result in a thin product.
An example of the second problem, i.e., preventing or minimizing syneresis (somewhat the opposite problem from undue thickening), may also be depicted by the Sirine et al composition. Sirine et al shows only the use of fumed silicas and only at levels of 5% by weight or less of the total composition. If a precipitated silica, which Sirine et al contend can be used in place of fumed silica, is used at such low levels, only thin, syneretic compositions result which are incapable of suspending abrasives, have poor viscosity and will no adhere to vertical surfaces. Syneresis may be observed to occur at levels as high as 50%. Further, nothing within Sirine et al indicates that the amounts of surfactant combined with the precipitated silica are critical to obtain an acceptable product.
Therefore, Sirine et al do not teach how to make either a cleaner which, upon storage will not set up or harden, or make a cleaner which avoids the opposite problem, i.e., thin, watery compositions which are unable to suspend abrasives. U.S. Pat. No. 2,257,467 issued Sept. 30, 1941 to Jacobson et al., describes a somewhat similar cleaning composition wherein silica is utilized along with a strong acid to provide a gel-like acid paste cleaner useful for cleaning hard surfaces. The product however is a paste of jelly, and contains no surfactants or abrasives.
Accordingly, the present invention is directed to cleaner compositions having desirable viscosity and minimal or no syneresis, which are capable of stably suspending abrasive particles. The inventive compositions additionally maintain these advantageous characteristics over an extended period of time. These cleaners will adhere to vertical surfaces because of their thixotropic characteristics and can provide good cleaning and high germicidal activity.